>It's not suprising that no one from /g/ has made a patch yet.

They did. Apparently the Gnome devs didn't want it. You can get it from the AUR.

https://gist.github.com/Dudemanguy/c172394e30e1e7d0f477ad15c...

https://aur.archlinux.org/packages/gtk3-patched-filechooser-...